1. Field of the Invention
This invention relates to a digital data conversion equipment and a method for the same, which are applicable to an interpolation of a thinned picture element in data conversion, up-conversion for converting a television signal with standard resolution into a television signal with high resolution and so on.
2. Description of the Prior Art
There are generally two kinds of systems for converting a digital video signal. One of them is a system for converting a signal whose resolution is high with respect to the space or time or a signal having a large amount of information into a signal of a low resolution. The other is a system for converting, on the contrary, a signal whose resolution is low with regard to the space or time or a signal having a small amount of information signal of a high resolution.
In the former case, a signal having inherently a large information amount is converted into a signal of a small information amount. For example, by properly thinning out a picture element information amount or field/frame information, a signal of a low space/time resolution can be easily formed.
The above example relates to what is called a down converter to, for instance, convert a video signal of a high definition (HD) system into a video signal of a standard definition (SD) system. Various kinds of techniques have already been proposed.
The latter case relates to up conversion to, for example, convert a video signal of the SD system to a video signal of the HD system. An example in which an electronic zooming process is executed or an enlargement of an image is performed is considered. In those examples, hitherto, information which inherently lacks is interpolated by using an interpolation filter and the interpolated information is used.
As still another example, there is a sub-sampling method for periodically thinning out pixel data in order to compress a recording/transmission data amount in the case where a capacity of the recording/transmitting system is limited. In this case, the images thinned out are interpolated on the reproducing/receiving side by using an interpolation filter.
However, there is a problem that the resolution of an output picture obtained by interpolation with a filter is degraded. For example, even if a HD television signal is formed by interpolating a SD video signal by a filter, an HD component (high frequency component) which is not present in an input SD signal is not reproduced. As a result, the spatial resolution of an output picture is lowered.